This invention relates to an arrangement including a nut and a locking pin therefor together with a method of visual inspection thereof.
Many assemblies in highly complex machines, for example, air craft include a large number of elements which are connected together. One common technique for fastening one element to another is to use a male threaded bolt or member on which a female screw threaded nut is placed and generally tightened. To prevent the nuts from becoming loosened during vibration, often a locking pin is applied to the combination to prevent the nut from rotating relative to the member except when the pin is removed.
In many cases, the nut is of the castellated type with the bolt member having a transverse hole so that the pin can extend between the castellations and through the hole to hold the nut against rotation.
Conventionally, a simple split pin is used which includes a pair of legs interconnected at one end of the pin by a loop member so the legs can pass through the hole in the bolt member and between the castellations and the loop member is received within the castellations following which the legs are bent apart to hold the device in place.
As will be apparent, devices of this type are used very widely in all types of different equipment.
Inspection of such equipment is in many cases mandatory and must be carried at regular intervals. The absence of a split pin of this type can have catastrophic results, possibly not immediately but at some future time when the nut has become sufficiently loosened that the elements can become disassembled leading to various failures of the assembly.
Without dissassembling and reassembling all of the parts, all that can be done for an inspection is for visual inspection to be carried out to check that the assembly has been properly completed and that all of the split pins are in place. In some cases the split pins are inadvertently omitted during manufacture or reassembly and in other cases they can become damaged or broken during use.
While such an inspection is relatively simple when carried out with a simple assembly of parts where the nut and split pin are readily apparent, it will be appreciated that in many highly complex machines such as air craft there are a large number of such split pin and nut combinations at various different angles and orientations within the assembly, many of which can be directly observed from an inspection panel but others can be in an orientation or position where it is more difficult to observe.
At the present time the various parts are manufactured from steel or other suitable materials which is often the same material as the other elements of the assembly so that it is very difficult by visual observation to determine the distinction between the various parts. Visual inspection is therefore very difficult and can in many cases overlook the fact that a essential split pin is missing leading to catastrophic consequences.